It is known that pelvic or hip abduction is an important condition for proper posture and stability. Hip abduction induces anterior pelvic rotation providing a wider base for more stable support of the upper body. Hip abduction also operates to bring the pelvis into vertical alignment with the spinal column.
The scapula (shoulder blade) is also a contributor to function of upper extremities. As with the alignment of the pelvis with the spine, alignment of the scapula with the upper arm bone and glenohumeral joint is necessary to perform mobile and coordinated tasks efficiently. Stabilization of the scapula requires highly coordinated and symmetric contractions of unrestricted muscles. High and/or wide seat backs restrict the range of the scapula, and may contribute to increase an upper thoracic rounding. This is commonly seen with people having rounded upper back and shoulder posture. Another result of high or wide seat backs may be seen in those having a head forward posture, with scapula abduction and shoulder internal rotation.
Current chairs having flat or bucketed seating surfaces facilitate posterior tilting of the pelvis, and thereby causing flattening of the natural anterior convex curvature of the lumbar spine. This promotes an overall flex position of the entire spine and possible cervical hyperextension. As a result, in order to move into an upright position to alleviate tension on the skeletal system, the person sitting in the seat must activate fast twitch fibers to move into an upright position. However, as fatigue sets in the skeletal system returns to the poor posture position. Additionally, many chairs are not adjustable for the torso and/or popliteal height. With chairs which are either too tall or too short of popliteal height, the deterioration of pelvic and spinal alignment typically occurs. This decreases the use of active movement against the surface, and decreases activation of the proprioceptive system which ultimately impacts attention levels, arousal, motor learning, head orientation and posture control. Further, chair depths, measured from knee to hip, are also too short for tall users.
The alignment of hip and spine along with the inhibition of posterior hip rotation has many advantages. For example, some studies indicate a direct correlation between productivity and posture/positioning. Moreover, ergonomic studies indicate that proper posture while in a seated position decreases back pain.
It would be desirable to create a seat assembly which overcomes these deficiencies.